[PATCH v2 02/12] drm/fb-helper: Avoid race with DRM userspace

[Noralf Trønnes]

Den 17.04.2019 15.26, skrev Daniel Vetter:
> On Wed, Apr 17, 2019 at 03:24:00PM +0200, Daniel Vetter wrote:
>> On Tue, Apr 16, 2019 at 08:46:24PM +0200, Noralf Trønnes wrote:
>>>
>>>
>>> Den 16.04.2019 09.59, skrev Daniel Vetter:
>>>> On Sun, Apr 07, 2019 at 06:52:33PM +0200, Noralf Trønnes wrote:
>>>>> drm_fb_helper_is_bound() is used to check if DRM userspace is in control.
>>>>> This is done by looking at the fb on the primary plane. By the time
>>>>> fb-helper gets around to committing, it's possible that the facts have
>>>>> changed.
>>>>>
>>>>> Avoid this race by holding the drm_device->master_mutex lock while
>>>>> committing. When DRM userspace does its first open, it will now wait
>>>>> until fb-helper is done. The helper will stay away if there's a master.
>>>>>
>>>>> Locking rule: Always take the fb-helper lock first.
>>>>>
>>>>> v2:
>>>>> - Remove drm_fb_helper_is_bound() (Daniel Vetter)
>>>>> - No need to check fb_helper->dev->master in
>>>>>   drm_fb_helper_single_fb_probe(), restore_fbdev_mode() has the check.
>>>>>
>>>>> Suggested-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
>>>>> ---

<snip>

> Ok, I read the later patches and you already have a commit() and a
> commit_force(). Count me convinced on all points.
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> as-is on this patch.
> 

Thanks. I want to apply this after the for-5.2 cutoff so we can get some
testing on this before it hits the world. I know from the timeline chart
that the cutoff is some time after -rc5, but I don't know _excatly_ when
that is. I looked at dim, but all I could glean from it was that it had
something to do with the state of a -fixes branch.

Noralf.